In the case where a liquid sample with components separated through liquid chromatography (LC) or the like is introduced in a mass spectrometer (MS) and detected, an ionization method, for example an atmospheric pressure chemical ionization method (APCI), and an electrospray method (ESI) is used in an ionization chamber. According to ionization methods, a liquid sample is ionized under pressure close to atmospheric pressure and thus, a middle chamber or the like is provided between an ionization chamber, where the pressure is high (that is, close to atmospheric pressure), and a mass spectrometric chamber under very low pressure (that is to say, close to a high vacuum), in order to secure a difference in pressure between the two chambers, so that a configuration where the degree of vacuum is increased in increments can be adopted.
According to such ionization methods, however, various types of fragment ions are not generated, as in electron impulse type ionization methods used for gas samples, and mainly ions having some relation to the molecular weight of sample molecules are generated, and therefore, information on the molecular weight of the liquid sample can be acquired in the mass spectrometric chamber, but almost no information can be acquired on the molecular structure of the liquid sample. As a result, a tandem mass spectrometer (MS/MS) is used as a mass spectrometer, and a collision chamber is provided between the two mass spectrometric chambers, and thus, ions having some relation to the molecular weight and collision gas collide in the collision chamber, so that a splitting reaction is induced in the ions having some relation to the molecular weight, and consequently, various types of fragment ions are generated, and as a result, information on the molecular structure of the liquid sample can be acquired in the mass spectrometric chamber in the rear stage.
In addition, a liquid chromatographic mass spectrometer having a collision cell where a quadrupole is provided inside the collision chamber has also been disclosed (see for example Patent Document 1).
FIG. 11 is a schematic diagram showing the configuration of an example of an electrospray mass spectrometer (ESI-MS), and FIG. 12 is a diagram showing the collision cell in FIG. 11. The ESI-MS is formed of an ionization chamber 10 where a nozzle 11 is provided and connected to the outlet end of the column of the liquid chromatographic unit, a first vacuum chamber 12, a second vacuum chamber 100 and a third vacuum chamber (mass spectrometric chamber) 18. A collision cell 31 is provided between a quadrupole filter 19-1 and a quadrupole filter 19-2.
In addition, a means for aiding ion transportation, referred to as ion ring or ion guide, which is provided so as to externally touch a circle having an optical ion axis as the axis (diameter: d1), is used in the first vacuum chamber 12 and the second vacuum chamber 100 in order to transport ions efficiently to the rear stage.
Furthermore, the ionization chamber 10 and the first vacuum chamber 12 are connected only through a desolvation pipe (heated capillary) 13 having a small diameter, and the first vacuum chamber 12 and the second vacuum chamber 100 are connected only through a skimmer 16 in conical form having a circular hole (orifice) 16a having a small diameter at the apex.
In addition, the second vacuum chamber 100 and the third vacuum chamber 18 are also connected only through a circular hole (orifice) 23a having a small diameter.
The collision cell 31 provided within the third chamber 18 is separated from the third vacuum chamber 18 by partitions 300-1 and 300-2 having circular holes (orifices) 300-la and 300-2a having a small diameter. Here, the circular holes 300-la and 300-2a are created in a plane forming an angle of 90 degrees with the direction in which ions progress.
Thus, a liquid sample is electrosprayed in the ionization chamber 10 through a nozzle 11, so that the sample molecules are ionized during the process in which the solvent in liquid drops evaporates. The microscopic liquid drops into which ions are mixed are drawn into the desolvation pipe 13 due to the difference in pressure between the ionization chamber 10 and the first vacuum chamber 12, so that the solvent evaporates during the process through which the liquid drops pass through the desolvation pipe 13 so as to be further ionized. A facing ion guide (also referred to as “ion lens” or “ion transport lens”) 14 is provided inside the first vacuum chamber 12, and an electrical field generated by the ion guide 14 aids the drawing in of ions through the desolvation pipe 13, and at the same time, ions converge in the vicinity of the orifice 16a (optical ion axis) of the skimmer 16.
Ions that pass through the orifice 16a due to the difference in pressure between the first vacuum chamber 12 and the second vacuum chamber 100 enter the second vacuum chamber 100, and furthermore, ions that pass through the orifice 23a due to the difference in pressure between the second vacuum chamber 100 and the third vacuum chamber 18 enter the third vacuum chamber 18.
A quadrupole filter 19-1 to which a voltage where a direct current voltage and a high-frequency voltage overlap is applied allows ions having a mass number (mass m/charge z) in accordance with the applied voltage to selectively pass within the third vacuum chamber 18.
Ions pass through the quadrupole filter 19-1 and then enter the collision cell 31.
An ion guide (also referred to as “ion lens” or “ion transport lens”) 37 is provided inside the collision cell 31, and ions accelerate as a result of the high frequency electrical field generated by the ion guide 37, and at the same time, the ions vibrate at a predetermined frequency while progressing so as to converge in the vicinity of the orifice 300-2a (optical ion axis) in the partition 300-2. At this time, a collision gas, such as He or Ar, is introduced into the collision cell 31 from an external gas reserve 26, so that ions and the collision gas collide, and various types of fragment ions are generated from the ions.
Ions that pass through the collision cell 31 (fragment ions) enter the quadrupole filter 19-2.
The operation of the quadrupole filter 19-2 is the same as for the quadrupole filter 19-1, and a quadrupole filter 19-2 to which a voltage where a direct current voltage and a high-frequency voltage overlap is applied allows ions having a mass number (mass m/charge z) in accordance with the applied voltage to selectively pass through.
As a result, ions that selectively pass through the quadrupole filter 19-2 reach an ion detector 20.
Here, the main working effects of the ion guide 37 are to cause flying ions to converge using an electrical field, in some cases to accelerate, and, various different types of ion guides have been proposed. One of these ion guides 37 is a so-called multi-pole type ion guide, where an even number of electrodes in columnar form which extend in the direction of the optical ion axis are provided at a distance from each other so as to externally touch the circle having an optical ion axis as the axis. In this multiple type ion guide, voltages where high-frequency voltages with a reversed phase overlap with the same direct current voltage (in other words, high-frequency voltages biased as a direct current) are applied to electrodes in columnar form which are adjacent along the circumference. As a result, the generated high-frequency electrical field allows ions introduced into the ion guide to progress while vibrating with a predetermined period, as well as to be transported efficiently to the rear stage.
In addition, in another example of an ion guide 37, a collective body of oval electrodes is used instead of electrodes in columnar form.    Patent Document 1: U.S. Pat. No. 4,234,791